Apparatus for vacuum drying



June 10, 1958 w, c, GATES I 2,837,831

' APPARATUS FOR VACUUM DRYING Filed March 15, 1955 V 4 Sheei-Sheet 2 Ij/pek /a'fi- W/fizar 6. 62756, v jj,% MW Z June 10, 1958 w, c, GATES v2,837,831

APPARATUS FOR VACUUM DRYING Filed March 15, 1955 fiqets-she g 3 5'0 55?/0- 559 ,g 2-1 June 10, 1958 v w. c. GATES 2,837,831

APPARATUS FOR VACUUM DRYING Filed March 15, 1955 4 Sheets-Sheet 4UnitedStates Patent APPARATUS FOR VACUUM DRYING Wilbur C. Gates,Flossmoor, lll., assignor, by direct and mesne assignments, of one-halfto Chicago Bridge & Iron: company, Chicago, 1th., a corporation ofIllinois, and one-half to Baerguard, Inc.,- Chicago, 111., a corporationof Illinois Application March 15, 1955, Serial No. 494,504

teatime or. 34-92 This invention relates to apparatus for'treating aflow able, liquid-absorbing solid material and more particularly totreating such material by moving itthrough a zone at a predetermined,controlled pressure condition.

The apparatus of this invention is particularly useful, for example, inthe drying'of a cereal such as wheat, rice, oats, and the like,particularly after such cereal has been vacuum puffed, in the drying oftobacco and in the drying of flour, powder, and the like.

As a result of the new apparatus of this invention, the followingadvantages are achieved when drying material: (.1) matting or fusing ofthe moistened solids is greatly reduced; (2) scorching of the materialis prevented; and (3) the rate of drying is increased as a result oftumbling of the material. If the tumbling is too violent or extreme,-undesirable breakage of the product will occur. The apparatus and methodof the present invention avoid such breakage.

Another advantage of the apparatus of this invention is thatsubstantially uniform, desired temper or liquid content of the treatedproduct is achieved. Careful heat profiling, i. e., regulation of thetemperature of the regions through which the material passes, furtheraids in achieving the desired degree of substantially uniform temper.

.All of these advantages are achieved by apparatus which can be operatedcontinually without time-consuming shut downs for charging the machinewith the material to be treated, removing the treated material, or anyother similar step.

When the apparatus of this invention is employed for drying material, itis preferred that the controlled pressure be a vacuum. Under suchcondition, the following additional advantages are achieved:' (1) becausthe vacuum condition increases the rate of evaporation, the temperatureneed not be r'aisedto a high figure; and (2) the quantity of materialthat can be dried during a given period of time by equipment of aparticular size is greatly increased; and, as a corollary, vacuum dryingequipment with a particular output rate occupies very much less spacethan would equipment required for drying at a comparable temperatureunder, for example, atmospheric conditions.

Following is a detailed-description of an embodiment of the apparatus ofthis invention which is directed to employment of the apparatus as adrier, and preferably as a vacuum drier. It is to be understood that theapparatus and method of this invention can also be employed to increasethe liquid content of the material by a controlled, predeterminedamount, whereby the temper of the treated material is substantiallyuniform.

The apparatus of this invention is illustrated in a preferred embodimentin the accompanying drawings and the method of this invention will bedescribed by reference to the drawings, in which:

Figure 1 is a side elevational view of the apparatus of this invention;

Figures 2A, 2B and 2C are enlarged longitudinal sectional views of theinput portion, middle portion and discharge portion, respectively, ofthe apparatus of Figure 1;

Figure 3 is a sectional view taken through the same apparatus along line3-3 of Figure 2A;

Figure 4 is a sectional view taken substantially along line 4 4 ofFigure 2A;

Figure 5 is a sectional view taken substantially along line 5-5 ofFigure 2A; and

Figure 6 is a sectional view taken along line 6 6 of Figure 2C.

Material treating chamber in the embodiment of the apparatus of thisinvention shown in Figure 1, material treating chamber 19, as hereshown, is a drier and slopes downwardly slightly from input port 11 todischarge port 12. A line 13 leads from a pressure control source, asfor example a vacuum pump (not shown), to the chamber 16. When a vacuumpump is employed, it is preferred that it be capable of main taining avacuum condition within the chamber 10 of as low as 0.1 inch of mercuryabsolute or lower.

The material to be dried, such as puffed rice, is introduced throughinput port it at the input end of the chamber 10 from a feed line 14,which is connected to the input port ii. In the event that a vacuumcondition is maintained in the chamber to and the other end of the feedline 14 connects with a vacuum chamber of a vacuum pufiin-g gun notshown in the drawings, introduction of the material will not impair thevacuum condition within chamber 10. However, if the other end of thefeed line 14 is at atmospheric pressure, suitable lock means should beprovided at the input port Zil to avoid any substantial impairment ofthe vacuum condition within the chamber 10. I

Lock out chamber 15 is provided at discharge port 1 2 to permit removalof the dried material without any substantial change in the pressurecondition within the chamber 10. The details of this lock out chamber 15are explained in more detail below.

Various other parts of the apparatus, such as the means for achievingheat profiling within the rotatable outer drum 2t and inner drum 28, asshownin dotted lines in Figure 1, will be described in detail below.

Rotatable drums Rot-atable outer drum 26 is best seen in Figures 2A, 2Band 2C which collectively show this drum in longitirdinal sectionrotatably mounted within chamber 10 As seen in Figure 3, outercylindiically-shaped drum 20 is mounted within chamber 16 on four pairsof revolvable Wheels 21, two pairs being positioned near one end of theouter drum 20 and the other two pairs, near the other end, as shown inFigures 2A and 2C. One wheel of each pair is located slightly to oneside of the bottom of the outer drum is.

Outer dnnn 2b is rotated on these wheel mountings by means-or" a motor23, mounted on the top of chamber 10. The drive axle of the motor passesthrough hermetic rotary seals 24. Gear 2% drives chain 26, which in turndrives gear 2? attached to the rotatable outer drum 2%).

Cylindrically sliaped inner drum 28 is rotatably mounted in spacedrelation to and within the rotatable outer drum 20 by studs 29 which arefixedly attached to the inner drum Z8 and the outer drum 2% at eitherend. As shown in Figure 3 inner drum 28 carries a group of tumblingvanes 30 (described in more detail below) some ofwhich cooperate withstuds 29 to aid in fixedly connecting the two drums.

The material to be dried passes through the annular space 31 between thetwo drums.

The slope of chamber 10 is determined by the de-' sired slope ofrotatable outer drum 20. This depends,

in turn, on the amount and type of material to be fed through thechamber 10, rate of feed, the temperature in the chamber 10, and therate of rotation of the drums. When vacuum puffed rice is to be driedunder a maintained vacuum condition in' the chamber of about 0.1 inch ofmercury absolute, it is preferred that the angle of downward slope forthe outer drum 20 be in the range of between one and four degrees.

Input end 32 of outer drum 20 is here shown as As previously stated, thematerial to be dried is in troduced into the input port 11 from feedline 14. From there it drops into an input chute 34, through which it isfed directly into input end 32 of the rotatable drum.

As shown in Figs. 2A and 4, feed wheel 35 is provided. This wheel isfixedly attached to inner drum 28 at its input end. Blades 36 of thisfeed wheel are here shown as fan-shaped and assist in feeding materialto be dried into annular space 31 at a uniform rate.

Tumbling vanes Both outer drum 20 and inner drum 28 are equipped withtumbling vanes. Outer tumbling vanes 50 are mounted on the interiorsurface of outer drum 20. It is preferred that the outer tumbling vanes50 be scoopshaped in cross section as shown in Figs. 3 and 5. As drum 20rotates, outer tumbling vanes 50 pick up material lying on the bottom ofthe outer drum and carry it up into the upper portion of the annularspace 31 enclosed by the inner and outer drums 28 and 20 respectively.The outer tumbling vanes in the embodiment shown run parallel to thelongitudinal axis of outer drum 20. However, they may be helical inarrangement if desired, or have any other suitable position so long aseach vane runs lengthwise of outer drum 20.

Inner tumbling vanes 30 are mounted on the outer surface of inner drum28. Like vanes 50, they run lengthwise of the drum on which they aremounted. In the embodiment shown, vanes 30 are T-shaped in crosssection, as best seen in Figure 3. They may, however, have a straightcross section or be of any other suitable shape, so long as they arespaced from vanes 50.

Tumbling action Referring to Figure 3, the fiowable material carried upfrom the bottom of rotating outer drum 20 by outer tumbling vanes 50will begin to spill out of these scoopshaped vanes at some point in theside portion of annular space 31. As any particular vane moves into theupper portion of the space enclosed by the two drums, it will spill outmore and more of the material it holds. By the time an outer tumblingvane reaches the top, and starts down on the other side, all of theparticles of material will have tumbled from the vane.

As the material tumbles out of vanes 50, any portion of the materialthat tends to form clumps by matting or fusing of the moist solidmaterial will tend to be separated upon falling onto the inner drum 28.This will speed up the drying process by permitting more rapidevaporation from the smaller particles of the material than would bepossible from larger clumps.

As best seen in Figure 5, outer, scoop-shaped tumbling vanes 50 extendinto the input end 32 of outer drum 20, a part of the drum into whichthe inner tumbling 4 vanes 30 do not extend. Employment of these outertumbling vanes 50 at the input end 32 of outer drum 20 results in moreextreme tumbling of the material at the input end of the drier. Sincethe largest clumps of particles are more likely to form in this regionbecause of the higher degree of moisture in the material at that stageand since the degree of moisture of the material is greatest, a greatdegree of tumbling in this region is preferred. These vanes, togetherwith the frustum-shape of the input end 32, also aid in achievinguniform feeding of the material into annular space 31. As shown inFigures 2C and 6, tumbling vanes 50 also extend into the output end ofrotatable outer drum 20. Instead of being scoop-shaped, it is preferredthat these vanes be in the form of relatively low ridges 52 protrudingfrom the inner surface of the outer drum 20. As a result, a mildtumbling action is achieved at this end of the drum and assists incausing the dried material to empty at a uniform rate into a surgehopper 53. This surge hopper is located immediately below the bottom ofthe output end of the outer drum 20.

Limitation of maximum free fall of particles It the tumbling produced byrevolving vanes 50 and 30 is too extreme, undesirable breakage of thematerial being dried might result. To avoid this, it is preferred thattumbling vanes 50 be relatively closely spaced, as shown in Figure 3.Thus, even if not otherwise defiected, particles of material fallingfrom vanes as high as position 50a or even position 50b in Figure 3 willhave a fairly limited free fall before landing upon the next lower vane.

However, particles carried by vanes 50 into the extreme upper portion ofthe space enclosed by drum 20 would, unless otherwise deflected, have afree fall of substantially the full diameter of drum 20. The arrangementof inner drum 28 and inner tumbling vanes 2d mounted thereon helps toavoid this by limiting the maximum free fall to which the material issubjected.

Any materials falling from outer tumbling vanes 50 after they havetraveled beyond about position 50]) will be caught by inner tumblingvanes 30 which have rotated into position 30a or beyond. Rotating innerdrum 28 and inner tumbling vanes 30 carry this material around to theopposite side of annular space 31 and there permit it to drop to thebottom of the drum.

Cross bars 51 of each inner tumbling vane 30 helps to confine materialwhich falls onto that vane as it rises on the ascending side. Further,it is seen that the opposite end of cross bar 51 operates on thedescending side to restrain the material from sliding freely offtumbling vane 30 to drop to the bottom of the drum. Thus, tumblingproduced by a drier carrying T-shaped inner tumbling vanes 30 issomewhat less active than if these vanes were simply straight members.

It is important to note that the distance between the inner surface ofthe outer drum and the outer surface of inner drum 28 may be varied,depending upon the type of material to be dried.

Outer tumbling vanes 50 and inner tumbling vanes 30 preferably areattached to their respective drums as by a continuous weld. Thisprovides maximum heat transfer to the material to be dried. For the samereason, it is preferred to construct the tumbling vanes in solid formand of a metal having high heat conductance.

Heating elements Referring to Figures 2A, 2B, and 2C, metal steam coils54, are fixedly mounted within the chamber 10 and surround the rotatableouter drum 20, being spaced therefrom. As here shown, these coils arearranged in separate banks surrounding different portions of outer drum29. Each bank is fed by a different one of lines 55a, 55b, 55c, 55d, and55e, which, in turn, is connected to a steam input feed line 16 throughvalves 18. Steam from a source not shown flows through the steam inputline 16, valves 18, into each bank of coils 54, and is then exhausted tothe atmosphere through line 17, which is connected to the terminal ofeach of the bank of coils 54. Condensate formed in the coils 54 isremoved through line 17, which vents to the atmosphere or a vacuumdepending on the temperature conditions and pressure in the coils. v

As a result, the amount of heat delivered to each bank and thus thetemperature of each portion of the outer drum 20 surrounded by a bank ofcoils 54, may be separately controlled andprofile heating of the drierachieved. In order to achieve maximum drying rate, it is preferred tosupply heat to inner drum 28. In the embodiment shown in Fig. 2C, innerdrum 28 is divided into two compartments by a wall 28a. Each compartmentis heated by means of input steam lines 56a and 56b, leading from asource of steam (not shown) through the end wall of the chamber 10,through a rotatable seal 58 (shown diagrammatically in Figure 2C)located at the closed end of the inner drum 28, and into the interior ofinner drum 28. Steam line 56b passes through a hole in the wall 28a andterminates in the front. compartment. Steam, flowing through input lines56a and 56b empties into the two compartments of inner drum 2S andprovides a separate source'of heat to each compartment as Well as to theinner vanes 30.

Spent steam and condensate formed in the interior I of the inner drum 28flows from the inner drum through an exhaust line 57, which leads fromthe closed end of each compartment of inner drum 28 through therotatable seal 58 through the wall of the chamber and to atmosphere or avacuum depending onthe temperature conditions and pressure in thecompartments.

Within the limits imposed by the physical charactris tics of theapparatus, the temperature of predetermined portions of the annularspace 31 may be controlled by regulation of the amount of steamintroduced into each bank of heating coils 54 and into the interior ofeach. compartment of the inner drum Z8.

Heated gas colmt'erflow Figure 20 shows another feature of the apparatusof this invention which may be used to greatly-increase the rate ofdrying. This feature is the introduction into chamber ltlof a heatedand/or dried gas flowing in the opposite direction from the flow of thematerial in the' Output l ck As previously explained, the dried materialflows from the output end 33 of outer drum 26 into the surge hopper 53.This hopper passes through discharge port 12 of'c'hamber It). Thematerial accumulates here until it is passed through lockout chamber 15for removal from the drier.

Bottom wall 63 of the surge hopper 53 is here shown as frustum-shaped;This forms an approach space through which-the material" must flow toreach the entrance-to lock out chamber 15.

A metal shield member 64,. here shown as comicallyshaped, is so adaptedthat its circular edge fits snugly against walls 63. When sofittedQ-th'is shield stops the flow of material towards entrance port 65of lock out chamber 15. The fit between shield 64 and wall 63 need -69,here shown as conical-shaped. A seal ring 70 is located about thecircular entrance to lock out chamber 15. Conical-shaped cover 69 is soadapted that, when in an inverted position and pressed into the entranceto lock out chamber 15, the outer surface of the cover 69 forms ahermetically tight seal with seal ring 70. In order to open and closethe entrance port 65, cover 69 is mounted on a rod 71 which terminatesat a piston 72. This piston is actuated by a powered cylinder 73, andmoves the cover up and down. The cover and sealing ring form a hermeticseal when the cover is in the up position. I

Discharge opening 74 of lock out chamber 15 is provided with a movablecover 76 bearing against a seal ring about the opening when in closedposition. Cover 76 can be opened and closed by means of movement of rod77a connecting the cover 76 with piston 77, which, in turn, is actuatedby a powered cylinder 78.

The same pressure condition as exists in the chamber 10 may be producedin lock out chamber 15 by means of a pressure control device (not shown)connected to the chamber by a line 79 leading from the lock out chamber15 through T -joint 80 and valve 81 tothe pressure cont'rol device. Thebranch of T-joint 8t) opposite valve 81 is connected through valve 82 tothe atmosphere.

.Dis'charge of dried material In operation, the desired amount of driedmaterial is permitted to accumulate in surge hopper 53. During thisperiod,lock out chamber 15 is connected'to the pressure control source(not shown) so that the pressure within the lock out chamber isapproximately the same order of magnitude as the pressure within chamber10. Covers 69 and 76 are, of course, kept closed during this operation.

When the material is to be passed into the lock out chamber 15, cover 69is opened, i. e., as here shown, moved downwardly, and shield member 64is raised from its closed positionof contact with approach wall 63. Thedried material may then pass freely into the lock out chamber 15.

When the desired amount of material has accumulated in lock out chamber15, shield member 64 is first returned to its closed position, cuttingoff the flow of the material through entrance port 65. Cover 69 isclosed after shield member 64 is moved into its closed position. By sodoing, no solid material can become entrapped between cover 69 and sealring 70 when the cover is moved into its closed position.

When cover 69 is in closed position, valve 81 is then closed, shuttinged the pressure control source and valve 82 is opened to the atmosphere.This brings lock out chamber 15 to atmospheric pressure. Cover 76 isthen opened to permit the dried material to flow out. When lock outchamber 15 is empty, the cycle may be repeated.

' Heat profiling As explained above, different amounts of steam may beintroduced through feed pipes 55a, 55b, 55c, 55d, and

552. The amount of steam introduced determines the 7 major heat transferfrom steam coils 54 is effected through radiation of heat upon the wallof outer drum 20.

At the input end of outer drum 20, where the degree of moisture is thehighest, it is preferred that the temperature be maintained at a higherlevel than in subsequent portions within annular space 31. As thematerial to be dried moves through annular space 31 towards the outputend of the chamber 10, it becomes progres of cereals, and particularlyvacuum pufied cereals, it is preferred to maintain a vacuum condition inthe chamber 10.

In turn, the carefully controlled evaporation rate permits control, towithin quite narrow limits, of substantially uniform temper or moisturecontent of the dried material discharged from the apparatus.

Additional accuracy of heat profiling is achievedby controlling theamount of steam delivered to each compartment of the inner drum 28through steam pipes 56a and 56b.

In the drying of tobacco, as well as cereals, it is often desirable totoast the substantially uniformly tempered fiowable material. This isreadily achieved by so controlling the amount of steam in at least thelast bank of coils 54, such as that fed by line 55c, and the amount ofsteam in pipe 56a leading into the end compartment of the inner drum 28,that the temperature of the end wall portions of outer drum and innerdrum 28 are high enough to toast the material to the desired degree. Byvirtue of the profile heating, the controlled pressure condition in thechamber 10 and the tumbling action, substantially uniform toasting isachieved.

Continuous operation The apparatus of this invention has been used todry pufied cereals, such as rice, wheat, etc., with excellent results.It may also be used very satisfactorily to dry tobacco in both shreddedand leaf form as well as powder and flour.

It is seen that all such materials may be dried in an uninterruptedcontinuous operation in which the moist, solid, fiowable material iscontinuously introduced at one end of the apparatus and is periodicallydischarged through discharge port 12 at the other.

The above detailed description of this invention is given for clearnessof understanding only. No unnecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

I claim:

1. An apparatus for treating flowable, liquid-absorbing solid material,which comprises: an elongated hermetically sealed material treatingchamber, means for.

controlling the pressure in the chamber, an input port at one end of thechamber and an output port at the other end of the chamber, an outerdrum and an inner drum arranged concentrically to each other'andlongitudinally aligned in the chamber, the outer drum having a receivingend and a discharge end, the inner drum being fixedly attached to theouter drum to form a drum unit, means for concentrically rotating thedrum unit,

the inner side of the outer drum and the outer side of the inner drumhaving means for tumbling material in the drum unit, means for feedingmaterial from the input port to the receiving end of the outer drum,means for progressively conveying the material from the receiving end ofthe outer drum, between the outer and inner drums, and out the dischargeend of the outer drum, means communicating with the discharge end andoutput port, and heating means provided in the chamber between the innerchamber wall and the outside of the outer drum, said heating meanshaving means for heating portions of the outer drum to differentpredetermined temperatures.

2. The apparatus of claim 1 in which the inner drum is closed at bothends and has heating means inside.

3. The apparatus of claim 1 in which the inner drum is shorter than theouter drum and is positioned intermediate the ends of the outer drum,the inner drum being closed at both ends.

4. The apparatus of claim 1 in which the receiving end of the outer drumis frustum shaped.

5. The apparatus of claim 1 in which the inner drum is shorter than theouter drum, one end of the inner drum being positioned inside the outerdrum and spatially positioned from the receiving end of the outer drum,and a feed wheel in the outer drum positioned about at the said end ofthe inner drum, said feed wheel being fixed to rotate simultaneouslywith the drum unit.

6. The apparatus of claim 1 in which the output port has meanscommunicating with a lock out chamber, said means containing at leasttwo valves, one of said valves being capable of stopping passage offlowable solid material without forming a hermetic seal, the second ofsaid valves being placed in said communicating means subsequent to thefirst valve and having means for creating a hermetic seal.

7. An apparatus for treating flowable, liquid-absorbing solid material,which comprises: an elongated hermetically sealed material treatingchamber, means for controlling the pressure in the chamber, an inputport at one end of the chamber and an output port at the other end ofthe chamber, an outer drum and an inner drum arranged concentrically toeach other and longitudinally aligned in the chamber, the outer drumhaving a receiving end and a discharge end, the inner drum being fixedlyattached to the outer drum to form a drum unit, said inner drum beingshorter than the outer drum, one end of the inner drum being positionedinside the outer drum and spatially positioned from the receiving end ofthe outer drum, means for concentrically rotating the drum unit, theinner side of the outer drum and the outer side ofthe inner drum havingmeans for tumbling material in the drum unit, feed wheel in the outerdrum positioned about at the said end of the inner drum, said feed wheelbeing fixed to rotate simultaneously with the drum unit, means forfeeding material from the input port to the receiving end of the outerdrum, means for progressively conveying the material from the receivingend of the outer drum, between the outer and inner drums, and out thedischarge end of the outer drum, and means communicating with thedischarge end and output port.

References Cited in the file of this patent UNITED STATES PATENTS907,925 Watters Dec. 29, 1908 1,196,376 Meyer Aug. 29, 1916 1,566,778Statham Dec. 22, 1925 1,681,690 Vernay Aug. 21, 1928 2,073,553 DienstMar. 9, 1937 2,207,987 Kent et al. July 16, 1940 2,602,498 Overton July8, 1952 FOREIGN PATENTS 44,284 Norway Aug. 1, 1927

